Material or shaders issue

Hi everyone, I'm new in Unity and I'm quite embarrassed for this question that seems to be ridiculous. Simply, when I assign a material to on object with a shader which is different from "Sprite Default" or "Sprite Deffuse", the object becomes invisible. Objects with these shaders seems to refuse any kind of light effect and they hide lights and particle effects even if i put these effects before the object. Probably this is a ridicolous issue, but i tried to read manuals and see tutorials and i don't get any result. This because i want to learn to apply lighting in Unity and create shadows...